Process for fabricating thin film multilayer modules using photosensitive epoxy dielectrics

Photosensitive epoxy resins are being developed to use as an innerlayer dielectric use in the printed circuit board industry. Using photoimageable dielectrics instead of traditional epoxy laminate is becoming a preferred method for fabricating high density circuit boards such as those used in multichip module (MCM-L) applications. Photoimageable epoxy has a significantly lower cost than polyimide or benzocyclobutene (BCB). If the material performance of the photoimageable epoxies is acceptable, the potential for lower fabrication costs for multichip modules on inorganic substrates such as ceramic, glass, and silicon is possible. The photoimageable materials evaluated in this study were a modified epoxy from Ciba Geigy, an acryclic-based epoxy from Enthone, and a polybutadiene-based epoxy from Shipley. They were evaluated for substrate adhesion, metal adhesion, and via formation. These materials had very good photoimaging properties and were capable of forming 10 μm features in a 5 μm thick dielectric layer. Multilayer modules with 25 μm design rules have been successfully fabricated on glass and ceramic substrates using the acrylic and polybutadiene as the innerlayer dielectric. These modules have not had dielectric, via, or metallization failures through high temperature reflows, humidity testing, or -55°C to 125°C temperature cycling